Highly dilutable polishing concentrates and slurries

ABSTRACT

The present disclosure provides a concentrate for use in chemical mechanical polishing slurries, and a method of diluting that concentrate to a point of use slurry. The concentrate comprises abrasive, complexing agent, and corrosion inhibitor, and the concentrate is diluted with water and oxidizer. These components are present in amounts such that the concentrate can be diluted at very high dilution ratios, without affecting the polishing performance.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to concentrates that can be diluted foruse in wafer polishing applications. In particular, the presentdisclosure relates to a concentrate that can be diluted as much as 50×or more, while still maintaining optimal or near optimal polishingperformance.

2. Description of the Related Art

The process known as chemical-mechanical polishing (CMP) involvespolishing different layers on semiconductor wafers, using a polish padand a slurry. Copper is a commonly used material for forminginterconnects in semiconductor manufacturing. Once a copper inlaidstructure is formed by, for example, a damascene process, the isolatedcopper wires are made by polishing and clearing copper and barrier metalbetween the inlaid wires. Copper and barrier layer CMP involvespolishing of copper and barrier layers. It is desired to polish thewafers at a high removal rate of material to enhance throughput, whilestill maintaining favorable wafer characteristics such as a low numberof overall defects.

A typical copper CMP process consists of 3 process steps. First, theelectro-plated copper overburden (up to 2 um in thickness depending ontechnology node) is rapidly polished down at a relatively high downforce, leaving some amount of copper until the deposition topography isfully planarized. (See FIG. 1) Throughput and planarization efficiencyand low defects are key needs. Then, the remaining copper overburdenafter full planarization during the first step is polished off at alower down force, with a stop on the barrier layer. The goal is to clearall copper from the barrier metal, but achieve significantly low dishingon the inlaid copper wire, with very low defects and improved surfaceroughness. Throughput is also important. This step can be combined withthe first step, depending on the polisher type or configuration. Lastly,the thin barrier layer left after the second step, generally Ta or TaN,or both, is polished off with significant topography correction, lowerosion and low defects. The slurry for the first two steps may be thesame or different. The barrier layer slurry, however, is usually adifferent composition.

Sometimes copper CMP slurries are made as concentrates. Theseconcentrates have the benefit of being cheaper to make and ship, whichreduces the cost of ownership (COO) of the CMP slurry. The customer cansimply add water and oxidizer at the point of use (POU), to form the POUslurry. One problem with this method, however, is that the concentratemust be properly designed to work well at the POU. By definition, aconcentrate has much higher amounts of all the components than would befound in the POU slurry. However, it is not possible to make anunlimitedly high concentrated polishing composition, as would bepreferable in a concentrate, because of stability and shelf life issues.In a colloidal slurry, stability is governed by particle surfaceeffects, which depend on the type, amount, and chemistry of theparticular particle. The higher the amount of abrasive in a slurry, themore the likelihood of instability. For example, if a POU polishingcomposition contains 1% abrasive, 1% removal rate enhancer, and 1%corrosion inhibitor, then a 10× Concentrate would be 10% abrasive, 10%removal rate enhancer, and 10% corrosion inhibitor, which could behighly unstable. Thus, CMP polishing compositions are made at aconcentrate level where they are stable for at least 6 months of shelflife.

The disadvantage to these slurries, however, is that they can not behighly diluted (i.e. on an order of 10× or 20×), which adds to the costof the CMP slurries ultimately needed for the polishing application. Inaddition, at higher dilutions, there is the risk that copper removalrates would be adversely affected, since at lower concentrations ofabrasive and removal rate enhancer, one skilled in the art would expectthe removal rate of copper to be less. The same holds true for anycorrosion inhibitors used in the slurry—if the amount of corrosioninhibitor is diluted too much, the resulting slurry may not preventcorrosion of the copper inlays as much as is desired.

The prior art clearly shows that the more a concentrate is diluted, themore the performance of the resulting POU slurry will suffer. Forexample, U.S. Pat. No. 6,428,721, to Ina et al., lists several exemplarycopper-polishing slurries in Table 1. The examples of that disclosureall comprise abrasive, hydrogen peroxide, alanine or glycine, and water.Table 1 clearly shows that the performance of the slurry drops offsignificantly as the slurry is diluted. When comparing Example 6 toExample 11, one can see that Example 11 is a 5× dilution of Example 6,since there is one-fifth as much abrasive in Example 11 as there is inExample 6. Consequently, Example 11 exhibits a drastically reducedremoval rate of copper when compared to Example 6.

Another reference showing the relationship between copper removal rateand is dilution is United States Patent Application Publication No.2008/0254628, to Boggs et al. FIGS. 9 and 10, and the accompanying textin ¶¶123-124, very clearly illustrate that as the dilution of a CMPslurry increases, the copper removal rate drops off dramatically.

This relationship between dilution and polishing performance is alsoillustrated in the data sheet for the CoppeReady® Cu3900 slurry, made byDA Nanomaterials, and available athttp://www.nanoslurry.com/datasheet/cu3900_product_sheet_final.pdf. Thedata sheet shows that when a slurry is diluted from a 4:1 strength to9:1, the removal rate can be very severely affected, and can drop asmuch as 50%, depending on the downforce applied to the slurry.

Thus, there is a need for a concentrate that can be used in CMPslurries, which is stable, yet does not suffer from decreasedperformance when diluted to high levels, as this is very desirable froma COO standpoint.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a concentrate that can be diluted toform a CMP slurry. The concentrate comprises abrasive, complexing agent,corrosion inhibitor, and water, in addition to other optionalingredients. To prepare a POU slurry based on this concentrate, the userwill add an oxidizer, and additional water, to the desired levels. Whenthese ingredients are mixed according to the formulas described below,the concentrate of the present disclosure can be diluted at a rate of upto 50× or more, while still maintaining excellent performance.

Thus, in one embodiment, the present disclosure provides a concentratefor use in a chemical mechanical polishing slurry, comprising about 0.5wt % to about 10 wt % of an abrasive, about 1 wt % to about 20 wt % of acomplexing agent, and 0.001 wt % to about 0.1 wt % of a corrosioninhibitor.

In another embodiment, the present disclosure provides a method ofpreparing a chemical mechanical polishing slurry. The method comprisesthe step of adding water and oxidizer to a concentrate, wherein theconcentrate comprises about 0.5 wt % to about 10 wt % of an abrasive,about 1 wt % to about 20 wt % of a complexing agent, and 0.001 wt % toabout 0.1 wt % of a corrosion inhibitor. The water and oxidizer can beadded to the concentrate in an amount governed by the formula:0.8≦[oxidizer]/ƒ≦2.0,

wherein ƒ=A+B*[complexing agent]^(C), wherein A is between 0.35 and 0.8,B is between 0.3 and 0.5, and C is about 1, and [oxidizer] and[complexing agent] are the amounts of the oxidizer and complexing agentin the chemical mechanical polishing slurry, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a copper CMP process;

FIG. 2 is a graphical representation of the concentrates of the priorart when compared to those of the present disclosure;

FIG. 3 is a plot of the ratio of a function of the amount of complexingagent to the amount of oxidizer in the concentrate, vs. the normalizedcopper removal rate of the slurry;

FIG. 4 shows a plot of the amount of complexing agent versus oxidizerfor several different embodiments of the present disclosure;

FIG. 5 shows the normalized removal rates for three CMP slurriesaccording to the present disclosure;

FIG. 6 shows a plot of the performance of a prior art slurry/concentrateaccording to the prior art at several dilution levels; and

FIG. 7 shows a plot of the performance of an additionalslurry/concentrate of the prior art; and

FIG. 8 shows a plot of the copper surface roughness of wafers polishedwith several different slurries according to the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides copper polishing CMP concentrates thatare highly dilutable, but retain key functional parameters such as highremoval rates, favorable wafer topography, and low and defects, such ascorrosion. The CMP concentrates of the present disclosure can be dilutedto up to 20× or more, and exhibit no significant change in performanceover less diluted concentrates, for example 10× or 5× slurries. This ishighly advantageous, in that users can minimize the amount ofconcentrate they need to keep on hand, thus keeping costs down, whilemaintaining the desired level of performance of the CMP slurry in thepolishing application. FIG. 2 shows this relationship graphically. Aspreviously discussed, it was thought in the prior art that the more theconcentrate was diluted, the more the performance parameters wouldsuffer, since the abrasive and removal rate enhancer concentrationswould decrease. The present disclosure, however, has provided aconcentrate that maintains strong performance parameters at very highdilution levels. The user can take the concentrate, and add oxidizer andwater at the POU, to the desired level.

In CMP, metal layers are removed by a combination of chemical andmechanical forces. With copper, dissolution (or ionization) takes placeat the surface of the copper. The removal of copper ions can be enhancedby a reaction with a complexing agent that can form a complex with thecopper layer. This complex is typically softer or more porous than thecopper layer before the CMP slurry is applied, so it can be removed moreeasily. An oxidizer is also useful in CMP slurries, as it forms a copperoxide layer, which is also more easily removed. When removing the bulkcopper layer, very high removal rates are needed, for example as high as10000 A/min, so it is desirable to use powerful complexing agents andoxidizers. If the chemistry is strong, however, it can be highlycorrosive to copper, and can create corrosion defects such as pitting orcopper loss. Thus, a proper corrosion inhibitor can be used in the CMPslurry. Abrasives are also a critical part of the removal of coppermaterials, and must have the proper hardness and morphology to removecopper oxide quickly. Ideally, a thin, soft, copper oxide and complexforms, and is rapidly removed without any corrosion, so it is importantto balance the four components described above.

Again, however, the more a solution is diluted, the more difficult itwill be to balance the amounts of these four components, leading to adramatic decrease in removal rate of the copper compounds.

The formation of the copper oxides and complexes depend on the strengthof the oxidizers and corrosion inhibitors used. A very strong oxidizerand corrosion inhibitor will result in thick hard oxide layer on thecopper. The passivation rate, or P, can be defined as the rate at whichthe oxide layer is formed, and is usually measured as a rate ofthickness increased per unit of time, for example Angstrom/min. Theremoval of this layer can be mechanical as well as chemical. Themechanical rate of removal of the complex and oxide layer, or M, isdefined as the thickness removed per unit of time, for exampleAngstrom/min.

Without being bound by this theory, the present disclosure believes thatwhen P>M, the process is chemistry driven and the copper removal ratesare lower than the ideal or peak values. When M>P, the removal processis primarily mechanical, and the copper removal rates are also lowerthan ideal or peak values. When P≈M, the process runs on a balance ofchemical and mechanical forces. The removal rates are is optimal andhigh.

The present disclosure provides a concentrate that takes advantage ofthese principles, and which can be diluted to a POU slurry. Theconcentrate comprises abrasive, complexing agent, corrosion inhibitor,water, and optional additional ingredients, in the amounts and asdiscussed below. To prepare the POU slurry, the user will add water andoxidizer to the concentrate. The amount of dilution that a user willrequire for a particular application will depend on several factors,though clearly, the less concentrate that is used to make a POU slurry,the more advantageous it is in terms of cost and material usage. A userwill dilute the concentrate to a point at which significant cost andmaterials savings are realized, but the resulting POU still performs tothe desired level.

To establish a relationship between the amount, or concentration, ofcomplexing agent, and the amount of oxidizing agent present in the POUslurry, the present disclosure first defines the following function:ƒ(complexing agent)=A+B*[complexing agent]^(C)A, B and C are constants for a particular formula. A can be from 0.35 to0.8, and has a unit of measurement identical to that for the complexingagent, in this case weight percentage. In one embodiment, B can be from0.3 to 0.5, or 0.33 to 0.46. C can vary slightly, but will remainabout 1. B and C are unitless constants. The use of brackets in thepresent disclosure, e.g. “[complexing agent]”, denotes the concentrationof the ingredient within the brackets, in this case the complexingagent. Unless otherwise specified, in the present disclosureconcentration is expressed as a weight percentage of the concentrate asa whole.

When preparing the POU slurry, the ratio of the amount of oxidizingagent to the function ƒ, i.e. [oxidizing agent]/ƒ, is known as the“oxidizer ratio.” The oxidizer ratio should be between about 0.8 andabout 2.0, or about 0.8 and about 1.3. The amounts of the oxidizingagent and the complexing agent in the POU slurry should be chosen sothat they satisfy this relationship. This will ensure that P≈M, which asdescribed above provides optimal conditions for the CMP process. Whenthese conditions are satisfied, the present disclosure has provided ahighly dilutable concentrate for use in copper CMP applications, whereincopper removal rates stay high and stable after diluting down to 20× orbeyond, wherein corrosion resistance remains high, and surface roughnessremains low. This is highly advantageous over currently availableconcentrates. The concentrate further comprises abrasives and corrosioninhibitors, as discussed below, as well as several optional additionalingredients such as surfactants, biocides, surface finishers, pHadjusters, and defect reduction agents.

The abrasives can be selected from the group consisting of alumina,fumed silica, colloidal silica, coated particles, titania, ceria,zirconia, or any combinations thereof. In one embodiment, the abrasiveis colloidal silica. The abrasives can be present in an amount of about0.5 wt % to about 10 wt %, or in an amount of about 1 wt % to about 5 wt%, each based on the total amount of concentrate.

The oxidizer can be selected form the group consisting of hydrogenperoxide, ammonium persulfate, silver nitrate (AgNO3), ferric nitratesor chlorides, per acids or salts, ozone water, potassium ferricyanide,potassium dichromate, potassium iodate, potassium bromate, vanadiumtrioxide, hypochlorous acid, sodium hypochlorite, potassiumhypochlorite, calcium hypochlorite, magnesium hypochlorite, ferricnitrate, KMgO₄, other inorganic or organic peroxides, or mixturesthereof. In one embodiment, the oxidizer is hydrogen peroxide. Theoxidizer can be present in an amount so that the POU slurry has about0.1 wt % to about 5 wt % of oxidizer, or from about 0.4 wt % to about 2wt %, so long as it satisfies the above-described relationship to theamount of complexing agent.

The complexing agent can be any compound that performs the desiredfunction. In one embodiment, the complexing agent is selected from thegroup consisting of organic acids and their salts, amino acetic acids,amino acids such as glycine or is alanine, carboxylic acids, polyamines,ammonia based compounds, quaternary ammonium compounds, inorganic acids,compounds with both carboxylic and amino functions, such asethylenediaminetetraacetic acid and diethylene triamine pentaaceticacid, or any mixtures thereof. In another embodiment, the complexingagent is glycine. The complexing agent can be present in an amount ofabout 1 wt % to about 20 wt %, or about 5 wt % to 13 wt %, each based onthe total weight of the concentrate.

The corrosion inhibitor can be selected from the group consisting ofbenzotriazole and its derivatives, tolyl triazole and its derivatives,and azoles, certain surfactants, or any mixtures thereof. In oneembodiment, the corrosion inhibitor is a benzotriazole derivative. Thecorrosion inhibitor can be present in an amount of about 100 ppm toabout 10,000 ppm, based on the weight of the concentrate, or a range ofabout 100 ppm to about 2000 ppm. The corrosion inhibitor can also bepresent in an amount so that the POU slurry has about 10 parts permillion (ppm) to about 1000 ppm, or from about 10 ppm to about 200 ppm.

Referring to FIG. 3, a plot of the oxidizer ratio vs. the normalizedremoval rate, i.e. the ratio of actual removal rate to the peak removalrate, is shown. When the oxidizer ratio is between 0.8 and 2.0, thenormalized removal rate is higher than 0.75, which is regarded as a highremoval rate range providing relatively stable and reproducible removalrate values. When the ratio is between 0.8 and 1.3, i.e. when P≈M, thenormalized removal rate is even higher, almost always over 0.8, and isoften at 1.0, meaning that the slurry is operating at the peak removalrate.

FIG. 4 shows a plot of the amount of oxidizer that can be present at agiven complexing agent concentration, according to one embodiment of thepresent disclosure, where the oxidizer ratio is 1.0. In the shownembodiment of FIG. 4, A is between 0.35 and 0.8, and B is between 0.33and 0.46. In the region of the plot between the two solid lines, theslurry will provide a normalized removal rate of 0.8 or greater. If theslurry has complexing agent and oxidizer concentrations that are outsidethis region, the performance of the slurry will drop. FIG. 4 also shows,in dotted line, the relationship between the concentrations ofcomplexing agent and oxidizer at the peak removal rate for the slurry.

FIG. 5 shows the normalized removal rates for three CMP slurriesaccording to the present disclosure. The tests were conducted using anApplied Materials Mirra polisher, a RHEM IC1010 polishing pad, and at a3 p.s.i. polishing down force. The shown compositions were preparedusing a concentrate comprising 13 wt % of complexing agent, 1 wt %abrasives, and a pH of about 7.5. Composition) is a 5× dilution of theconcentrate of the present disclosure. As can be seen, even whenComposition 1 is diluted 7× (i.e., a 35× dilution of the concentrate),or even 10× (i.e., a 50× dilution of the concentrate), the removal rateremains very high. The 50× dilution CMP slurry still operates at 90% ofthe removal rate of the 5× dilution CMP slurry.

By contrast, FIG. 6 shows the performance of a prior artslurry/concentrate according to the prior art. Comp28 is ComparativeExample 2 of Table 1 in U.S. Pat. No. 6,428,721, which was discussedabove. The data shown have been reproduced using Comp28 with variousdilution ratios. When Comp28 is diluted, there is a dramatic drop-off inthe performance—at just 2× dilution, the normalized removal rate hasalready dropped below 0.8. This effect is even more pronounced whenComp28 is compared to a more concentrated formulation of itself, asshown in FIG. 6. Clearly, then, the performance of the slurries of theprior art suffers significantly when the slurries are diluted.

FIG. 7 shows an even more drastic example of a prior art CMP slurrywhose removal performance suffers dramatically when it is diluted. FIG.7. Comp6 is example 6 of Table 1 in U.S. Pat. No. 6,428,721. When Comp6is diluted 5×, the normalized removal rate drops off almost 80%. Again,this shows that the performance of prior art slurries sufferssignificantly when they are diluted.

FIG. 8 shows surface roughness data for several slurries according tothe present disclosure. As can be seen in the Figure, slurries dilutedto various levels all exhibited similar surface roughness data, withinacceptable noise levels. There is a minor drop in the surface roughnessof the 10× slurry, but this is not considered statistically significant.

It should be noted that in the present disclosure, dilution ratios ashigh as 20× were achieved without any loss of functional performance atall, and higher ratios, such as the 50× described above, were achievedwith minimal performance loss. Higher dilution rates are also possibleif one accepts lower optimal copper removal rates. If, instead of 80% ofthe peak removal rates, one can accept 60%, the dilution ratio can beincreased, to as much as more than 50×.

The following list defines some of the terms used in the presentdisclosure.

-   -   highly dilutable: 5× or more dilution    -   complexing agent for copper: a compound forming a soluble or        insoluble complex with copper    -   oxidizers for copper: chemicals that oxidize the copper atoms to        a higher valence state    -   corrosion inhibitor: chemicals that protect the copper surface        from corroding    -   abrasive: solid particles that aid in mechanical removal of        wafer surface    -   normalized removal rate: the ratio of a particular removal rate        to that of a reference, such as the peak removal rate, or the        removal rate of a baseline composition    -   peak removal rates: the highest removal rate for a given slurry    -   oxidizer level for peak removal rate: the oxidizer concentration        that corresponds to the peak removal rate    -   oxidizer ratio: the ratio of the peroxide concentration to the        concentration of the complexing agent    -   optimally high copper removal rates: removal rates within 75% of        the peak removal rates

The present disclosure having been thus described with particularreference to the preferred forms thereof, it will be obvious thatvarious changes and modifications may be made therein without departingfrom the spirit and scope of the present invention as defined in theappended claims.

1. A chemical mechanical polishing slurry, comprising: a) a concentrate,comprising: about 0.5 wt % to about 10 wt %, based on the total weightof said concentrate, of an abrasive; about 1 wt % to about 20 wt %,based on the total weight of said concentrate, of a complexing agent;and a corrosion inhibitor; b) water; and c) an oxidizer, wherein saidwater and said oxidizer are present in the slurry in an amount governedby the formula:0. 8≦[oxidizer]/f≦2.0, wherein f=A+B*[complexing agent]^(c), wherein Ais between 0.35 and 0.8, B is between 0.3 and 0.5, and C is about 1, and[oxidizer] and [complexing agent] are the amounts of the oxidizer andcomplexing agent in the slurry, respectively.
 2. The slurry of claim 1,wherein said abrasive is selected from the group consisting of alumina,fumed silica, colloidal silica, coated particles, titania, ceria,zirconia, and any combinations thereof.
 3. The slurry of claim 1,wherein said complexing agent is selected from the group consisting oforganic acids and their salts, amino acetic acids, amino acids, glycine,alanine, carboxylic acids, polyamines, ammonia based compounds,quaternary ammonium compounds, inorganic acids, compounds with bothcarboxylic and amino functions, ethylenediaminetetraacetic acid,diethylene triamine pentaacetic acid, and any mixtures thereof.
 4. Theslurry of claim 1, wherein corrosion inhibitor is selected from thegroup consisting of benzotriazole and its derivatives, tolyl triazoleand its derivatives, and azoles.
 5. The slurry of claim 1, wherein theconcentrate is highly dilutable.
 6. The slurry of claim 5, wherein theconcentrate is diluted to a level of at least 10×, to form the slurry.7. The slurry of claim 5, wherein the slurry is used to remove a copperlayer from a substrate, and the chemical mechanical polishing slurryremoves said copper layer at a rate that is at least 75% of a peakremoval rate of the chemical mechanical polishing slurry.
 8. The slurryof claim 1, wherein said oxidizer is present in an amount of about 0.1wt % to about 5 wt %, based on the total weight of the slurry.
 9. Theslurry of claim 1, wherein said oxidizer is present in an amount ofabout 0.4 wt % to about 2 wt %, based on the total weight of the slurry.10. The slurry of claim 5, wherein the concentrate is diluted to a levelof at least 20×, to form the slurry.
 11. The slurry of claim 1, whereinsaid corrosion inhibitor is present in an amount of about 0.001 wt % toabout 1 wt %, based on the total weight of said concentrate.